At the buzz of a rattlesnake, the heart races, and the adrenalin flows. Our response is primal, physical.

But rattlesnakes also exert a power over the imagination. For many, the fear of rattlesnakes is mixed with fascination.

Rattlesnakes are impressive predators, and they play an important role in the West Texas ecosystem.

Rattlesnakes first appeared about 4 million year ago. They’re the most recently evolved snake – and the most highly specialized.

They’re unique to the Americas, found from Canada to Argentina. But West Texas is truly rattlesnake country. The majority of rattlesnake species live in the American Southwest and Mexico.

Rattlers rely on complex adaptations to survive in this unforgiving land.

Chief among them are “pit organs” – heat-sensing organs between the snake’s eyes and nostrils. The organs give rattlers infrared vision, allowing them to find prey in the dark of night. Rattlers identify rodent trails by scent. They “smell” with their tongues. Then, they bide their time.

Michael Haynie is an interpretive ranger at Guadalupe Mountains National Park.

“They’re mainly a sit-and-wait predator,” Haynie said. “Rather than actively going out and seeking prey, they’ll find an area with lots of scent trails, maybe a good spot to hide, and then they’ll coil up – and it might be days before they strike it just right. In pitch dark they can see, like a flashing bullseye right in front of them.”

Rats and mice form the mainstay of the rattler diet. Studies show that a snake can consume 14 percent of the rodents within its home range.

You wouldn’t welcome a rattler at your doorstep, but they do provide a service. Rodents are vectors for disease such as Hantavirus and Chagas. And rattlesnakes help reduce rodent populations in the backcountry.

With the prey in its sights, the snake strikes. Here, another distinctive adaptation is on display.

The more ancient venomous snakes – cobras, coral snakes, the mambas of Africa – have fixed fangs. But a rattler can fold its fangs against the roof of its mouth.

“That allows the fang to be much longer,” Haynie said. “So when they go to strike, their mouth opens about 180 degrees, the fangs pop out into place, and it’s just a quick injection of the venom, deeper into the prey, so it dispatches the prey faster – whereas Old World snakes and fixed-fang snakes have to almost hold on and chew a little bit.”

The Trans-Pecos is home to six rattlesnake species. The most abundant is the western diamondback, sometimes called the “coon tail,” for the black-and-white stripes on its tail. Diamondbacks range across many habitats – from desert scrub and mesquite grasslands to pine-oak forests.

A second rattlesnake – the black-tailed – favors rocky canyons and mountains. It’s at home in the region’s highest elevations, among pines and Douglas firs. A third, the rock rattler, grows to only two feet in length. Gray in color, it blends into the boulders and cliffs it calls home.

Less common rattlers include the desert massasauga, a small snake that inhabits sandy areas. The prairie rattler prefers dry areas, with grassy cover.

Then there’s a rattler with a particularly fearsome reputation – the Mojave. While Mojaves in California and Arizona have a greenish tint, here in West Texas they’re virtually indistinguishable from diamondbacks.

Mojaves won’t pursue a person – but they are testy, Haynie said.

“The Mojave rattlesnake is known to strike out,” he said. “It wouldn’t come at you, but it’s less likely to tolerate somebody stepping by it if they didn’t see it.”

The effects of hemotoxins are slow, and painful. But the neurotoxins are quick-acting – and can paralyze a victim’s diaphragm and inhibit breathing.

Venom varies seasonally and by individual snake. But Mojave venom is thought to have a higher concentration of neurotoxins than that of other rattlers.

Rattlesnake bites are by no means common. Of the millions of hikers in the 40-year history of Guadalupe Mountains National Park, not one has been bitten by a rattlesnake.

But rattlesnakes are a real hazard of the West Texas outback. A bite victim should seek medical attention immediately. Few bites are fatal – but the effects can be serious, including tissue damage and even limb loss.

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